Variable: any characteristic or phenomenon that can vary across organisms, situations, or environments.

 

Variables can be manipulated or measured.

 

Three categories of variables:

 

·        Independent variable (usually manipulated)

·        Dependent variable      (usually measured)

·        Subject variable (usually selected, may involve measurement)

 

 

OPERATIONAL DEFINITIONS

 

Two types of definitions are usually found in empirical research papers. Conceptual definitions, which resemble dictionary definitions that refer to the general concepts, are often presented in the introduction. Operational definitions, which define traits in concrete, step-by-step physical terms, are usually presented in the section on method.

 

An operational definition specifies the operational measures, which we use to define a concept or variable.  It must be presented in great enough detail so another researcher could repeat it to replicate the study.

 

 

Operational definitions should be provided for all declared variables.  The following example does not describe the specific physical actions taken in the presence of the experimental participants.

 

“The stress-producing condition for the experimental group was a mild verbal threat given by the experimenter.”

 

Better: “In order to produce the stress-producing condition for the experimental group, a male experimenter who was dressed in a white doctor’s jacket seated the participants.  He introduced himself as a medical doctor and stated that for the purposes of the experiment, ‘You will receive a mild electric shock while we measure your blood pressure.’”

 

 

Types of variables:

 

·        Discrete: a variable that consists of separate, indivisible categories, so that no values can exist between two categories.  E.g. type of disorder, major

 

·        Continuous: a variable that has an infinite number of possible values, and can be represented by fractional or whole units.  E.g. scores on a test, reaction time

 

Variables can also be categorized as

 

·        Qualitative: a variable that varies in kind.

 

·        Quantitative: A variable that varies in amount.

 

 

Ways in which the desired variation in an IV can be achieved

·        Presence versus absence

·        Amount of variable (how many levels)

 

·        Type of variable (assign labels)

 

 

Concrete ways in which variation can be achieved

 

·        Experimental manipulation (controlled adjustment of the IV)

 

Instructional manipulation

 

Event manipulation

 

·        Individual difference manipulation (results in an ex post facto type of study)

 

 

Factors Affecting Our Choice of Variables to Manipulate or Observe

 

·        Research Tradition

Our variables may be similar to those used in previous studies

 

·        Theory

Theories may suggest certain variables to be included

 

·        Availability of new Techniques

Sometimes a new technique is developed, allowing us to manipulate a variable that we could not in the past

 

·        Availability of Equipment

The variables we manipulate may be limited by the equipment available to us


The Dependent Variable

 

Must be sensitive enough to show variations in performance as a result of variations in the IV.

 

            Ceiling effect: Performance high at all levels of the IV

 

            Floor effect: Performance low at all levels of the IV

 

Must be appropriately related to the IV (e.g. split-brain studies)

 

 

Types of dependent variables

 

 

 

 

 

 

SELF-REPORT MEASURES

 

The most direct way to assess a construct, a hypothetical attribute or mechanism.

 

However, it is very easy to distort such measures.

 

Types of questions:

 

a.             Open-ended: Respondents are asked to answer a question in their own words.

E.g. "What is your opinion of your employer's affirmative action policies?"

 

b.            Closed-ended with a limited set of response alternatives.  A list of choices is given and they check the desired alternative.

E.g. "One of the major reasons for getting married is to have children."

                        Agree _________   Disagree_______

 

c.             Likert-type Scales: Respondents circle a choice, a number on a scale, or check a point on a line that best reflects their opinion.

E.g.  "The US Congress should increase spending on social programs."

 

Strongly disagree  Don't know            Strongly agree

 

·        Make sure to avoid pitfalls in constructing questions, such as the following:

a.       Double-barreled questions (that ask two different things).  E.g. "Do you believe there are equal opportunities for minorities and women at your place of employment?

 

b.       Loaded questions (that contain emotionally charged language). E.g. " To what extent do you think the values of the Ku Klux Klan are alive and well in the South?"

 

1                      2                      3                      4                      5

 

not                               uncertain                                              very much

alive                                                                                         alive

 

Above question could be rephrased as:

"To what extent do you think support for racial segregation still exists in the South?

 

1                      2                      3                      4                      5

 

very weak                uncertain                                              very strong              

support                                                                                support

 

c.       Leading questions (that bias people to respond in a given way).  E.g. "I agree with the popular view that our current foreign policy is flawed."

Better: "Our current foreign policy is flawed."